1. Field of the Invention
The invention relates to a process for preparing organyloxysilyl-terminated polymers which have increased stability toward atmospheric moisture, and to crosslinkable compositions comprising such polymers.
2. Background Art
Moisture-crosslinkable formulations are well known, particularly those which are based on silyl-functionalized polymers. In turn, preference among such polymers is given to those having terminal alkoxysilyl groups, since the cleavage products are noncorrosive and do not raise toxicological concerns. The silyl-functionalized polymers are prepared by conventional methods. One example is the reaction of polymers which have end groups having active hydrogen with isocyanates, particularly isocyanatoalkylalkoxysilanes. The reaction may be carried out with or without catalysts which promote isocyanate reaction. EP 931 800 A describes the preparation of silane-functional polyurethanes from hydroxy-functional prepolymers and, for example, isocyanatopropyltrimethoxysilane under anhydrous conditions, and preferably under an inert gas atmosphere in order to prevent premature hydrolysis of the alkoxysilane groups. EP 372 561 A describes the preparation of a silane-crosslinkable polyether which has to be stored with exclusion of moisture, since it vulcanizes with or without silane condensation catalysts. The fact that this preventative measure is independent of the preparation process of the silane-crosslinkable polyether can be taken from EP 397 036 A1. In the latter publication, a polyether, for example one with allyl end groups is reacted with an alkoxyhydridosilane. The publication indicates that premature vulcanization proceeds even without a silane condensation catalyst.
Known silane condensation catalysts include numerous compounds, for example dialkyltin(IV) compounds such as dibutyltin dilaurate; various metal complexes (chelates and carboxylates), for example of titanium, bismuth, zirconium, amines and salts thereof; and other known acidic and basic catalysts as well. Reference may be had, for example to EP-A 673 972 and EP-A 538 880. However, known catalysts which promote the isocyanate reaction with hydroxyl groups are often those which also promote silane condensation, for example dialkyltin(IV) compounds and metal complexes (chelates and carboxylates) of bismuth and zinc, or tertiary amine compounds.
The disadvantage of all known processes for preparing silane-crosslinkable polymers is due to the fact that the polymers have to be handled under conditions including exclusion of moisture. However, in industrial practice this is associated with a high degree of complexity and is therefore expensive.